This invention relates to stable, cold water soluble, ready for use starch aldehyde compositions, their method of preparation and the use thereof as strength additives in papermaking.
The term "paper", as used herein, includes sheet-like masses and molded products made from fibrous cellulosic material which may be derived from natural sources, synthetics such as polyamides, polyesters, rayon and polyacrylic resins as well as from mineral fibers such as asbestos and glass. In addition, paper made from combinations of cellulosic and synthetic materials are applicable herein. Paperboard is also included within the broad term "paper".
The preparation of aldehyde containing starches and other polymers and the use of such aldehyde derivatives as wet and dry strength additives in the paper industry is well known. Oxidative and non-oxidative methods have been used to introduce aldehyde groups into polysaccharides such as starch. The oxidative methods have included: a) treatment of starch with alkali metal bromite or hydrobromite under carefully controlled conditions as disclosed in U.S. Pat. No. 3,553,193 issued Jan. 5, 1971 to D. H. LeRoy et al.; b) oxidizing a carbohydrate with an alkali metal ferrate as shown in U.S. Pat. No. 3,632,802 issued Jan. 4, 1972 to J. N. BeMiller; c) enzymatically oxidizing hydroxypropyl galactoglycoside starch ethers or ethyl galactoglycoside starch ethers with galactose oxidase as disclosed in U.S. Pat. No. 4,663,448 issued May 5, 1987 to C. W. Chiu; and, d) treatment with periodic acid or as disclosed in U.S. Pat. No. 3,086,969 issued to J. E. Slager on Apr. 23, 1963 which shows the preparation of dialdehyde polysaccharide using periodic acid and U.S. Pat. No. 3,062,652 issued on Nov. 6, 1962 to R. A. Jeffreys et al. which shows the preparation of dialdehyde gums using periodate or periodic acid.
Non-oxidative methods for preparing aldehyde containing starches include a) the reaction of granular starch with an unsaturated aldehyde as disclosed in U.S. Pat. No. 3,519,618 issued Jul. 7, 1970 to S. Parmerter, and b) the reaction of an amidated starch or glucopyranosyl compound with glyoxal as shown in U.S. Pat. No. 3,740,391 issued Jun. 19, 1973 to L. Williams et al.
Aldehyde containing polymers used as strength additives in paper are disclosed in U.S. Pat. Nos. 4,508,594 and 4,605,718 issued on Apr. 2, 1986 and Aug. 12, 1986 respectively to R. Jansma et al. which show aldehyde containing vinyl polymers. Glyoxalated (meth)acrlyamide polymers are disclosed in U.S. Pat. No. 5,320,711 issued to D. Dauplaise et al. on Jun. 14, 1994.
U.S. Pat. No. 3,269,964 issued to J. Curtis on Aug. 30, 1966 discloses a water dispersible composition which is the reaction product of a dialdehyde polysaccharide and a condensation product of dicyandiamide and formaldehyde. U.S. Pat. No. 3,299,052 issued to J. Curtis on Jan. 17, 1967 also discloses a water dispersible composition which is the reaction product between a dialdehyde polysaccharide and a hypochlorite oxidized polysaccharide.
Many of the wet strength additives currently used in the paper industry are synthetic polymers which are aqueous, ready-for-use liquids. However, they generally have limited storage stability and shelf life.
One of the problems associated with the use of aldehyde containing derivatives is the possibility of crosslinking and instability that they possess.
U.S. Pat. No. 4,675,394 issued to D. Solarek et al. on Jun. 23, 1987, discloses aldehyde containing starch derivatives, their preparation from acetals and their use as paper additives. As disclosed in the patent, problems associated with the use of aldehyde derivatives in active form can be avoided by providing the stable acetal form of the corresponding starch which can be converted to the starch aldehyde by cooking under acid conditions just prior to its use. However, this involves an extra conversion step which must be carried out by the user-customer.
What is desired is a ready for use starch aldehyde product which is stable and avoids the need to combine it with other components or the necessity of performing an extra processing step prior to its use in papermaking or other application.